Our boxes are packed by weight to account for any empty or under filled packets that might get packed along with the good ones. So there may be extra packets in any box that will be empty or under filled.
There are millions of packets coming off the packaging machines. The packing line has blowers that try to blow the empties off the conveyor belt, but inevitably empties do get packaged.
There is another consideration if ALL the packets seem under filled. Please read this article to make sure you are buying the right product.